1985 johnson 150(not gt)

[south599]

anyone ever determine the power these motors put out at the prop? i have heard rumors that they were rated at the crank for 150 but by the time it got down to the prop there was a lot of power lost?

[terry taylor]

Do you know if it is a cross-flow ,or loop charged power head thanks ?

[south599]

Crossflow

[Forkin' Crazy]

About 7% loss what I was told. 67mph is doing pretty good with that rig IMO!

[south599]

alright thats not to bad but that puts it around 140 prop? im considering putting the 175 carbs on it. if im thinking right this'll put the hp at the prop somewhere between 155- 165? im also factoring in that the engine is almost 30. thank you i have been working hard to get it dialed in. that 67 was not at WOT i just ran out of driving talent . id say it would have hit 70 at least that day.

[neveredge]

The 85 GT150s were rated at the prop not the powerhead and should be making close to 165hp, hence the GT moniker. 83 and earlier motors were powerhead rated. You can thank Yamaha for prop shaft rated outboards. They got sued for doing it but won their case so shortly there after everyone went to propshaft ratings.

I believe the carbs on the flat back 175 and the GT150 are the same. There wasn't much difference between the flat back 175 and GT150.

If you have a standard 150 and not a GT then it is probably only making 140. The pic in your avatar shows a standard cowling so I assume it is not a GT.

My suggestion is to find a good 2.6GT and put it on there. Just about the same weight but it will make about 220 at the prop.

[south599]

it isn't a gt. But this motor runs so well and i've talked to several johnson guys and the difference between the 150's and flat back 175's were the carbs. they'll swap over and put me close if not above a true 150 as according to the prop.

[Forkin' Crazy]

If I am not mistaken, the 150 GTs had 2 5/16" carbs, same as the 175s.

[south599]

i have been told that as well